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Influence of Nutrient Enrichment on Structuring Diatom Communities in a Glacial Meltwater Stream, Mcmurdo Dry Valleys, Antarctica

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Influence of Nutrient Enrichment on Structuring Diatom Communities in a Glacial Meltwater Stream, Mcmurdo Dry Valleys, Antarctica INFLUENCE OF NUTRIENT ENRICHMENT ON STRUCTURING DIATOM COMMUNITIES IN A GLACIAL MELTWATER STREAM, MCMURDO DRY VALLEYS, ANTARCTICA By Joshua Darling University of Colorado at Boulder A thesis submitted to the University of Colorado at Boulder in partial fulfillment of the requirements to receive Honors designation in Environmental Studies Defended 31 March 2015 Thesis Advisors: Diane McKnight, Civil, Environmental and Architectural Engineering, Committee Chair Dale Miller, Environmental Studies Sarah Spaulding, Institute of Arctic and Alpine Research (INSTAAR) © 2015 by Joshua Darling All Rights Reserved ABSTRACT In the arid McMurdo Dry Valleys of East Antarctica, glacial meltwater streams flow for 6-10 weeks during the austral summer. Harbored in these meltwater streambeds are diatom communities, which are part of a microbial mat matrix. These mat assemblages endure desiccating winters and become reactivated upon rehydration during the austral summer. Water is considered the major limiting resource in the dry valley stream ecosystems, and the variable flow of meltwater has been shown to regulate the biomass and growth of these algal mats. However, other environmental variables could influence the structure of these mat communities. In this thesis, the influences of nutrients are examined as a regulatory control on diatom community structure. This thesis draws from previous experimentation using Nutrient Diffusing Substrates (NDS) with nitrate and phosphate amendments that were left in Green Creek for algae to colonize. Characterization of diatom communities that grew on NDS units showed that nitrate enrichments significantly altered diatom relative abundance, with an increase in Fistulifera pelliculosa to 21% relative abundance in nitrate treatments compared to other nutrient amendments, which had less than 5% F. pelliculosa abundance. Other nutrient amendments showed only a marginal influence on diatom relative abundance. In addition, nitrate and phosphate amendments showed greater average diatom densities relative to the control treatments, with the greatest densities occurring in nitrate amendments. These results suggest that nutrients influence diatom growth and accrual, although stream hydrology and geomorphology likely have a greater influence on regulating the structure of these diatom communities within the microbial mat matrix. Moreover, the results from this thesis can help to predict the response by diatom communities to expected landscape changes in McMurdo Dry Valley streams as a function of climate change, such as increase flow and subsequent nutrient enrichment. KEYWORDS: diatoms, algae, nutrients, climate change, colonization, streams i PREFACE I want to thank Dr. Diane McKnight for providing me with many opportunities to explore aquatic ecology through hands-on learning in her lab. The advice I have received from Dr. McKnight has been particularly valuable, and I wish to extend my many thanks. In addition, I want to recognize Dr. Sarah Spaulding for her passion and expertise in the world of diatoms and algae. Further, Dale Miller has provided excellent advice and encouragement throughout the duration of this project. Tyler Kohler, who initially conceived of this project and completed the in-field portion, made the work pertaining to this thesis possible. I am very grateful for the guidance and expertise that Tyler has brought to this project. In addition, I want to thank Dr. Pat Kociolek, who allowed me to take part in his freshwater phycology class to learn more about the taxonomy of diatoms. ii CONTENTS CHAPTER 1 | INTRODUCTION .................................................................................................................. 1 PURPOSE AND SCOPE .................................................................................................................................... 1 FORMAT OF THESIS ....................................................................................................................................... 3 CHAPTER 2 | BACKGROUND ..................................................................................................................... 4 GREATER MCMURDO DRY VALLEYS ECOSYSTEM ................................................................................................ 4 MCMURDO DRY VALLEYS STREAMS ................................................................................................................. 6 ALGAL MAT COMMUNITIES: CHARACTERISTICS AND DISTRIBUTION ....................................................................... 8 DIATOMS ................................................................................................................................................... 11 MCMURDO DRY VALLEY STREAM DIATOMS .................................................................................................... 13 CHAPTER 3 | METHODS .......................................................................................................................... 19 GREEN CREEK: SITE DESCRIPTION .................................................................................................................. 19 NDS COLONIZATION .................................................................................................................................... 22 DIATOM ENUMERATION ............................................................................................................................... 24 DIATOM COMMUNITY CHARACTERIZATION AND ANALYSIS ................................................................................. 24 Species Presence ................................................................................................................................ 25 Diversity ............................................................................................................................................. 25 Density ................................................................................................................................................ 25 Relative Abundance ............................................................................................................................ 26 CHAPTER 4 | RESULTS ............................................................................................................................. 27 SPECIES PRESENCE ...................................................................................................................................... 27 DIVERSITY .................................................................................................................................................. 28 DENSITY .................................................................................................................................................... 29 RELATIVE ABUNDANCE ................................................................................................................................. 31 CHAPTER 5 | DISCUSSION ....................................................................................................................... 35 APPENDIX .................................................................................................................................................. 38 BIBLIOGRAPHY ......................................................................................................................................... 40 iii iv Chapter 1 | INTRODUCTION Purpose and Scope The purpose of this thesis is to assess how nutrient loading influences the establishment of diatom (Bacillariophyta) taxa in a glacial meltwater stream located in Taylor Valley, of the McMurdo Dry Valleys, Antarctica. Diatoms are a type of unicellular algae and are fundamental primary producers found in marine and freshwater systems the world over. The algal group is valued as a useful bio-indicator of environmental change. And, in regions sensitive to small climatic changes, such as the McMurdo Dry Valleys (MDV), diatom monitoring can be a useful tool for understanding the ecological response to chemical and physical controls in a dynamic system. This thesis addresses the response of colonizing diatom assemblages to nutrient enrichment to better understand the ecological structure and function of these diatom communities. For most aquatic systems, it can be expected that an increase in the major limiting nutrients for that system will result in increased growth. However, is not always explicitly known how diatom communities will respond to nutrient loading—especially in the context of the oligotrophic Antarctic streams, where diatom communities represent only a small portion of the microbial mat biomass, and where nutrient concentrations in the mat matrix can be significantly controlled by the pre-existing microbial mat communities. Many of the diatom taxa present in the MDV streams are considered endemic to the MDV region and have evolved in harsh environmental conditions. Furthermore, understanding how the MDV stream diatom community structure is influenced by nutrient enrichment will provide more insight into the microbial mat ecology of the MDV region. The stream of interest in this thesis, Green Creek, is nitrogen limited (Gooseff et al., 2004), 1 and so it can be hypothesized that diffused nitrate treatments will result in stimulated algal growth. Yet, it is still unknown how the community structure of these diatom assemblages will change with regard to different treatments. This thesis will examine the significance of nitrate and phosphate to the
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